Is it necessarry to create theory/infrastructure to prevent people from creating AI incompatible with a safe model (if we create one)?
It seems impossible to prevent that. If someone can make a safe AI from scratch in the near future, then someone else can make a dangerous AI from scratch as well. If all that's needed is a computer (or eventually a robot) it will be really hard to stop people from creating one.

Banning computers? Maybe it could prevent it, but that comes with quite a few negative sides as well.

A law against creating AIs? Would be really hard to follow-up, and what about the AIs people want to make to be used for something "good"?

And even if we could come up with a good set of laws they probably wouldn't be introduced in all countries, and also be really hard to follow up.

I guess we just need to make our own defence mechanisms which can fight unsafe AIs (physically or virtually) when that time comes.